Wireless Sensor Networks (WSNs) are becoming an integral part of ubiquitous computing, a growing trend involving embedding processors in all types of objects and allowing them to communicate usually on an ad hoc basis. In general, a large number of wireless sensors collect and transmit information about the environment to an application that uses the information. The wireless sensors are placed in the environment and connect to a data network to communicate the data they sense as wireless sensor nodes. The data is transmitted to applications that use the data. Such applications may be anywhere geographically and readily accessible over the Internet.
Wireless sensors nodes may have a temperature sensor, a microphone, a pressure sensor, an optical sensor, a camera, an accelerometer, or any other suitable sensor on the device. Wireless sensor nodes may be distributed in an environment in large numbers and communicate as a wireless sensor network. A wireless sensor network may also connect to other types of network nodes lacking sensors, but providing functions useful to the application or to the environment, or for supporting data communications in the network.
Wireless sensor networks (“WSN”) may provide data to a wide variety of applications and environments using a large and dynamic number of sensor nodes. For example, wireless devices are being deployed in aviation application environments. Low power heterogeneous sensors numbering in the hundreds or thousands are wirelessly networked to form a predominantly asymmetrical flow of data from sensors to data sinks. The data sinks may be servers, or other computing resources, that integrate the sensor data into higher intelligence about the environment being sensed. Ad hoc protocols based on IEEE 802.15.4, such as Zigbee, for example, have been developed in the past decade to partially address the deployment of WSNs. However, there are shortcomings that can be attributed to the non-determinism and overhead associated with such dynamic ad hoc wireless environments. Aviation applications, for example, demand a higher level of network availability, deterministic timing, and predictable data packet throughput in order to reach required levels of application reliability on the order of 10−5 failures per flight hour.
The typical ad-hoc, event driven mode in which wireless sensor nodes attempt to communicate data with no predetermined message timing incorporates Carrier Sense Multiple Access (CSMA) schemes. Networks utilizing CSMA schemes may use collision avoidance or collision detection to minimize the number of failed transmissions in the communication medium. However, as the number of network nodes increases, and as the network nodes use more and more of available bandwidth, the number of collisions increases resulting in reduced network availability and increased latency. The required levels of reliability become more difficult to maintain.
As such, there is a need for a system and method for controlling access to a communication medium that maintains high availability and reliability as the number of nodes in the network continues to grow.